1. Field of the Invention
The present invention relates to a yaw rate estimating apparatus for estimating a yaw rate of a vehicle based on a difference in wheel speed between left and right wheels.
2. Background Information
There has been known a yaw rate estimating apparatus that estimates a yaw rate based on a difference in wheel speed between left and right wheels, which occurs when the vehicle is making a turn and the left and right wheels move following different trajectories. Such yaw rate estimating apparatus for a vehicle is disclosed in the Japanese unexamined Patent Publication No. 10-175528.
It has been conceived that such estimated yaw rate can be used for detecting malfunction of a yaw rate sensor by comparing the estimated yaw rate with a detected yaw rate of the yaw rate sensor. In such case, it is desirable to estimate the yaw rate while the left and right wheels are in non-controlled state in order to assure the accuracy of the estimated yaw rate. However, the load of the vehicle tends to move outward while the vehicle is making a turn. Consequently, a tire diameter of the outer wheel, which is located radially farther from the center of rotation of the vehicle, becomes smaller, while a tire diameter of the inner wheel becomes greater. Therefore, if the yaw rate is estimated without taking such effect into consideration, the estimated yaw rate will become greater than the actual yaw rate, since an additional wheel speed difference induced by the tire diameter difference is added to the wheel speed difference due to the difference in trajectories.
In view of the above, there exists a need for a yaw rate estimating apparatus which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
Accordingly, one object of the present invention is to provide a yaw rate estimating apparatus capable of estimating the yaw rates more accurately.
Another object of the present invention is to provide a yaw rate estimating apparatus which estimates the yaw rate based on the wheel speed difference between the detected left and right wheel speeds, and which is corrected based on the lateral acceleration, so that an error in the estimated yaw rate due to the tire deformation during a turn can be advantageously precluded. As a result, the more accurate estimated yaw rate can be obtained.
To achieve the objects of the present invention, a yaw rate estimating apparatus is provided for a vehicle having a right wheel and a left wheel. The yaw rate estimating apparatus comprises a right wheel speed sensor, a left wheel speed sensor, a vehicle status detector, a lateral acceleration device and a control unit. The right wheel speed sensor detects a right wheel speed of the right wheel and generates a right wheel speed signal. The left wheel speed sensor detects a left wheel speed of the left wheel and generates a left wheel speed signal. The vehicle status detector indicates a current state of a selected parameter of the vehicle. The lateral acceleration device determines a lateral acceleration of the vehicle and generates a lateral acceleration signal. The control unit is operatively coupled to the vehicle status indicator and the right and left wheel speed sensors to initially estimate a yaw rate of the vehicle based on a difference between the right wheel speed and the left wheel speed from the right and left wheel speed signals in response to the control unit determining the vehicle is a non-controlled state from the vehicle status indicator. The control unit corrects the estimate of the yaw rate based on the lateral acceleration signal to determine and output an estimated yaw rate.
The forgoing objects of the present invention can also be attained by providing a yaw rate estimating apparatus for a vehicle having a right wheel and a left wheel, the yaw rate estimating apparatus comprising a right wheel speed detecting means for detecting a right wheel speed of the right wheel; left wheel speed detecting means for detecting a left wheel speed of the left wheel; non-controlled state detecting means for detecting whether the vehicle is in a non-controlled state; lateral acceleration obtaining means for obtaining a lateral acceleration generated on the vehicle; yaw rate estimating means for computing an estimated yaw rate of the vehicle based on a difference between the right wheel speed and the left wheel speed if the vehicle is in the non-controlled state; and correcting means for correcting the estimated yaw rate based on the lateral acceleration to output a corrected estimated yaw rate.
The forgoing objects of the present invention can also be attained by providing a method of estimating a yaw rate of a vehicle having a right wheel and a left wheel, the method comprising providing a right wheel speed sensor and a left wheel speed sensor; determining whether the vehicle is in a non-controlled state; detecting a right wheel speed of the right wheel through the right wheel speed sensor; detecting a left wheel speed of the left wheel through the a left wheel speed sensor; obtaining a lateral acceleration of the vehicle; computing an initial estimation of a yaw rate of the vehicle based on a difference between the right wheel speed and the left wheel speed if the vehicle is in the non-controlled state; and correcting the initial estimation of the yaw rate based on the lateral acceleration to determine an estimated yaw rate.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.